Fear of the Dark
by TulipsandTulle
Summary: Sherlock/John, established relationship, disregarding events from Reichenbach on. John begins to notice strange behaviors in Sherlock, and the truth changes everything he ever thought about their future. Eventual major character death.
1. Chapter 1

It didn't start out this way. A cigarette here, a missed meal there. It wasn't until one night, after a difficult case, that John noticed the beginnings of a problem.

"Sherlock, you gonna touch that egg roll?" John muttered through a mouthful of greasy pork fried rice. The chopsticks lay abandoned in the paper takeaway bag, along with the tiny packets of sauces. The detective rolled his eyes, pushing his barely touched plate toward his flatmate.

With short, clipped movements, Sherlock pulled a scratched cigarette case from his pocket and lit up. It took John all of a second to pull it away and snub it into the remains of the Szechuan pork. "Oi, you great git, I live here too." John's eyes narrowed in realization. "You were supposed to have quit."

Sherlock huffed, putting his hand into his pocket as if to shield the case from John's awareness. "You're a doctor, John, you must know the likelihood of taking up the habit increases after each unsuccessful attempt to—"

"Show me your arms." John growled and reached over the table to grasp at the tall man's arms. Sherlock's sleeves gave way under his fingertips; no track marks. The detective sucked at his teeth in irritation, plucking at the fabric to right it. His ice blue eyes looked back down to the treatise on herbs sitting within reach. John's eyes softened, and he reached across the table, more carefully this time. "Sherlock, I trust you with my life. I just can't be too careful, yeah?"

As John waited for the man to warm back up to him, he noticed his hand shaking beneath his own. "Hey, you alright, love?"

Sherlock pulled his hand away, his back to John. "I'm off to bed. Goodnight, John."

John sighed, the takeaway soon forgotten. He pushed his chair away from the table, following the detective to the bedroom in silence. The taller man got to the door and turned the knob, budging it open with a foot. John closed the door quietly, watching as his partner shucked his dress shirt and pants, leaving them in a heap on the floor. That was unlike Sherlock, he usually put them neatly away as soon as his clothes left his skin; it was one of his many eccentricities, something that made him Sherlock, and John immediately noticed the change while he tucked himself under the covers, curled into himself.

John picked up the discarded clothes, laying them on top of the hamper with his own. A light from the street shone past the edge of the curtain, illuminating just the curly mop of hair on top of Sherlock's head. John crawled into bed, sidling up to the silent detective and pressing his chest to Sherlock's smooth, pale back. He kissed a beige freckle, just below his nape, and curled a protective arm around the brunet.

"You mind telling me what's wrong?" John whispered, unwilling to break the burgeoning silence in the room. The worn duvet felt soft against John's back, and the room seemed harsh and cold, in comparison. He tangled his feet with Sherlock's, a habit he picked up after months of sharing a bed with the lanky man. His toes barely reached Sherlock's ankles, but he felt cozy, just the same.

Sherlock feigned sleep, until a brush of John's lips over his scapula made him sigh.

"I'm just fine, John. I promise. My body's needs caught up with me, is all. It was a rough case, what with the estranged father's affair, and the daughter's prescription drug smuggling ring—"

"I know, love, I was there, remember?" John smiled fondly. "How did you find out about that, anyway?"

"Her boots. They were far too expensive, when compared to her bag and her cheap haircut. It was obvious she was getting the money from somewhere other than the family's antiques business." John could almost hear the exasperation in Sherlock's tone, the "it-was-hardly-a-stretch-and-you-should-have-known" lilt to his voice, all too familiar.

"Alright, I'll let you sleep, then," John murmured, burying his nose into Sherlock's curls.

All through the night, he felt the occasional twitch in Sherlock's foot, and thought nothing of it. He imagined he was dreaming of the chase, his coat billowing behind him, and John not far behind.


	2. Chapter 2

Sherlock wanted to go out to dinner one night. In the throes of an experiment, he suddenly stood and declared "John, get your coat. We're going out."

John smiled. "What for? Are the tumours giving you trouble?" Sherlock removed his blood-spattered safety glasses, wrinkling his nose at the blood smeared on his thumb.

"No, they're quite sufficient. The passing fancy to go out for some real dinner was just too good to pass up." He grinned, that infectious eye-crinkling smile that John couldn't help but return. Sherlock bent to scoop up his phone and his magnifying glass, returning them to the pockets of his Belstaff. On his way to their room, Sherlock brushed his hand over John's shoulder, a familiarly cool touch. The blond man seized the other's hand, pulling him down to press a kiss to his lips, finding a clean expanse of skin in the corner of his lips.

"I'll find my wallet, you hurry and get cleaned up, you silly man." John brushed their noses together, reveling in the clean, smoky smell of Sherlock's skin. He stood, looking up into those damnable eyes, with their greens and blues and greys, and wondered how many times it would take before he had those colors memorized. "Where is it we're going?"

"A surprise." Sherlock turned with a cheeky swish of his hip, and John laughed. Something new every day, with this man. He hardly expected grand gestures and planned nights out when he began his relationship with Sherlock Holmes, but he saw that Sherlock's inherent need to please was fed by John's presence in his life. Sherlock was given to theatrics, and John not only accepted them, but appreciated them. John knew that he was one of the few Sherlock cared enough to share his favorite things with; Lestrade wouldn't understand, his parents were too traditional, and Mycroft was too busy with his own life to traipse all over London with his little brother. The only one left was John, long-suffering John, who'd nearly died at the hands of murderers and murderesses, a fledgling under Sherlock's capable wing.

Sherlock emerged from his room as John mused, his back to the detective and attempting to dust off his corduroy blazer for likely yet another night at Angelo's. Angelo was a kind man, and more than willing to serve the two (whatever they liked, on the house, for Sherlock and his date), but John could only order the cavatelli primavera so many times in a month. "Darling, do you remember where I put my shoes, the brown ones?"

Sherlock tsked, stopping John's hands from behind while he tried to badger the button through the hole and replacing the fumbling fingers with his own. He buttoned the jacket quickly, and John looked down to see Sherlock's arms dressed in an immaculate black suit jacket, stark white shirt, and complete with the admittedly flashy diamond cufflinks they'd received from a past client.

"Oi, I thought we were going to dinner?" John asked, looking up to the taller man's face. He brushed a hand over the pressed lapels and the neat coif of Sherlock's hair. "What's all this for?" he smirked. "Don't tell me it's all for me…"

"Sorry to disappoint, love, but I told you I had a surprise in mind." Sherlock pulled the blond by his arm to the door, John more than willing until he realized his state of dress.

"I can't go out to some posh place looking like this, I'll look a fool!" John pulled himself from Sherlock's grasp, chuckling in disbelief at his lover's scoff. "You were going to let me leave the house like this, weren't you?"

Sherlock slipped into his shoes. "Well, I don't see any issue. You look gorgeous, as always." The words were said with no sarcasm, no hint at malice or falsehood. John reached for the man's hand, touched.

He pressed the knuckles to his lips. "Ten minutes, if I'm late you can take Mrs. Hudson."

Sherlock waved a hand dismissively. "She'd take hours if I asked her out to dinner. Go on."

John put a touch of cologne on, dabbing just above his pulse point and on his wrists. He readjusted his jacket, feeling ridiculous in his untailored suit. The pants were just a tad too long, and they made him look like a child playing in his father's shoes. He sighed, patting himself down to right his suit. He heard a light tap on the door.

"You look fine, John. Come on out, it's just dinner." The infuriating man always knew just what he was thinking. He'd probably deduced John's trepidation from the amount of time spent rifling through his closet or some other such nonsense. There was no reason to fret, he told himself. This was Sherlock. The only one he was there for was Sherlock. He opened the door, almost whacking the detective in the face with it. If it weren't for his quick reflexes, he'd be sporting quite a goose egg. John's hands fidgeted at his side with embarrassment while Sherlock smiled knowingly.

"C'mon, relax." Sherlock held his hands in his own, his eyes softened with concern. "We can stay in, order takeaway if you like. However…." Sherlock leant into John's ear. "I know you're not one to back down before a challenge."

With that in mind, John stood straighter, dragging the younger man enthusiastically to the door, bringing a hand to his arse to lead him out.

Once the cab pulled away, John could take full stock of the building before him.

Quaint, unassuming, but carefully painted to let off an air of warmth and welcome. The words outlined in bronze above the door were in French, and John let his hands wander over the lush plants in boxes over the fence. The dark wood doors, glass panes set into them, opened to reveal a lush carpet and a warm lighting reminiscent of a wood fire. Sherlock's hand on John's lower back was reassuring in such a new space. The blossoms frosting the branches of ornamental trees beckoned to the ceiling, and a sandy stone fireplace looked over the room, crackling away as if it were a part of the hushed conversation.

Once the thin maître d' seated the two and brought them their wine (Sherlock chose a lovely red that John couldn't quite get enough of), the two ordered. John picked a mint pea soup with gnocchi that Sherlock insisted was one of his favorites, and Sherlock chose a braised leg of lamb with rosemary and snap peas. The two chatted over their wine, Sherlock making sly deductions about the woman with the fur stole, the man with the amethyst pin in his lapel, and the two women who both wore teal gowns. The wine, being potent and of the highest quality, got to John's head faster than he expected. A warm sensation spread through his chest, down his legs and to his fingers. The smile on Sherlock's face was quirked to one side, and he offered his plate to John whilst dipping his soup spoon into the blonde's soup and nicking a gnocchi. John, however, didn't much mind. The flavors of mint, garlic, rosemary, and fresh peas were light and insistent on John's tongue, and while Sherlock seemed to have little mind for the food, John finished what was left of both of their dinners while Sherlock swished the wine in his glass and watched the look of rapt enjoyment on John's face. John noted that, while Sherlock's eyes were always a sight, the look of them now was his favorite. They were blown wide with the alcohol, and the aquamarine of his eyes was dazzling in the candlelight.

Sherlock noticed John's prolonged staring and chuckled. "I bet there's something you've failed to notice, what with your ogling."

"An' what's that?" John asked, his buzzed head feeling consonant sounds to be unnecessary.

Sherlock pointed up to the tall ceiling, John's eyes following. The ceiling was anything but; it was a large window, a skylight, right above their heads. John looked up and saw the stars, twinkling and glinting right through the glass. Sherlock attempted to control his laughter while he ordered a tiramisu to share, the waiter smiling good-naturedly at the sandy blond.

As soon as the dessert was finished, the two boys paid and were on their way, hailing a cab and piling in before they caught a chill in the cool night air. Their hands settled on Sherlock's knee, Sherlock rubbing circles into John's hand with his thumb. "How was that for a surprise?" Sherlock murmured, leaning into John. John missed the look of trepidation in Sherlock's eyes, the wry grin that had nothing to do with his blood alcohol content.

"It was perfect. I'm glad you decided to put down that experiment." John smiled his head on his partner's shoulder. "That dessert was damn rich, though. I thought it'd take hours to finish."

The cab slid to the curb in front of their flat on Baker Street. Sherlock unfurled from his seat in the cab, reaching the door and stumbling on his way up the steps. He caught himself on the railing, his eyes shut momentarily to focus his vision. However, as John gripped his arm, concern in his tone as he asked the younger man if he was alright, the steps and the front of their building took on a cardboard-flat quality. An icy moon loomed over the night, over London, and Sherlock felt the cold run down his spine, only to coalesce in the pit of his stomach.


	3. Chapter 3

A shrill hum ran through Sherlock's head. No no no. Not now. His vision was swimming, and he held to John's arm tightly. He wanted to look left, to John's eyes, to see the reassurance and warmth there. His eyes had other ideas. It was as if they were moving past a film of molasses. When they finally reached John's face, Sherlock relaxed. John's frantic voice cut through the static and the panic ebbed.

"… Sherlock?! Oi, look at me, love. Yes, right there." John whipped his keychain from his pocket, using the tiny LED light to shine in Sherlock's eyes. The pupils were slow to constrict. John checked Sherlock's pulse; it was a frantic flutter under his forefinger. Sherlock's eyes moved slowly, in erratic circles. John budged the door open, wanting to get Sherlock out of the cold air and into the comfort of the flat, as quickly as possible.

"John, help me up the stairs, I'm doubting my ability to do so on my own, at present…" Sherlock ventured to find John's shoulder, gripping it tightly.

John, understanding that Sherlock would only ask for his help with such a task if he was truly incapable, pulled the taller man's arm round his shoulder. He led him up the stairs to their flat, his feet slightly unsteady under the combined pressures of Sherlock's weight and his alcohol-dabbled system. "Up we go, love." He murmured, almost more to himself than to his lover. He fished in his jacket pocket for his keys again, smiling wryly as the detective held them up. At least my pickpocketing skills are sharp, Sherlock thought.

Once inside the flat, John positioned Sherlock on the couch, once again shining the light into his eyes to check their response. They were close to normal, now. Sherlock, however, felt uneasiness settle in his lungs. His vision wasn't improving. He reached out, experimentally, to touch the silver pin on John's lapel, finding his fingers brushing his arm instead. John watched his efforts with growing worry.

"Love, did you have too much to drink?" John felt his cheeks, and they were cool to the touch. "I know your tolerance isn't quite as high as mine, but I didn't think—"

Sherlock muttered something under his breath, his eyes scrunched closed to avoid the look he knew he would see cloud John's eyes. Pity. Fear. Disbelief.

John's eyebrows knitted. "Say that again?"

"Huntington's, John. It's Huntington's."

John stood stock-still, his jaw tightening. His mouth worked away, but no sound would come out, nothing but an abrupt gasp. He was drowning.

He held his arms tight to his chest, holding his heart together. "Say that again."

"Huntington's disease. It's a genetic disorder which affects the brain, it degenerates. The CAG repeat on chromosome 4—"

John held up a hand. "Studied at Bart's, trust me, I remember." He took a deep, shaky breath, one he'd been holding in, knowing it would lead to sobs. "You're sure?"

Sherlock looked to the floor. "I've been noticing an impairment in my depth perception. My balance is off. I've been more impulsive, less …" John watched him reach for words. "Eloquent, for one. I can't think, John. It's so damn slow, like grasping at straws." The desperation in his voice was apparent, as was the raw fear. Sherlock's mind was the only thing he had any trust in.

John imagined the soft, pink hemispheres of Sherlock's brain shrinking, decaying… He'd seen it before, while he was in med school. It would be his mood, first. He'd sleep for most of the day one day, then stay up for the next several days. He'd be irritable. He'd lose the ability to swallow. He'd fidget, restless. First, as it worsened, he'd forget the names of things, small things, like the model of a car going down the road. Then he'd lose the word for car. He'd forget his life, his past. He'd be like an old man, confused and disoriented, asking John who he was, where he was. He'd jerk, his brain sending faulty impulses to the limbs. He'd lose control of his speech, unable to form simple sentences, let alone "I love you". John held his head in his hands. "How could you keep this from me?"

Sherlock reached out to the blond man, thinking better of it and retreating into himself.

There was no cure. They could slow it down, keep the snapping, growling dog at bay, keep it from eating away at the raw flesh of Sherlock's brain. But they had maybe a few years. The onset could be late and slow, or quick and violent depending on the number of CAG repeats. The average age of onset, John recalled, was somewhere between 30 and 40. John bit his lip. If it was starting now, just beginning near the end of that span, he could have anywhere from ten to twenty years.

John knelt down so that he was face to face with his lover, pressing a hand to his cheek. The grim line of his mouth turned up at the corners. "Darling, how long have you seen these symptoms? Can you pick a date out?"

Sherlock sighed, resigned. "Late twenties, the mood abnormalities started." John's sudden intake of breath was exactly what he expected. "I thought it was just a result of my above-average mind. However, the fidgeting, the restlessness, that wouldn't correlate to my IQ. I started putting the pieces together a month or so ago, when the lack of focus began. I did some research at Bart's, went through some patient files. It's an earlier age of onset than most, John, it usually begins in the mid-thirties. That means that the CAG repeats, they're far more than most, the descent will be rapid…" Sherlock's hands clenched. "I've noticed the space between lines of thought, John, they're longer. My mind palace, the secret passageways and tunnels are caving in. I feel like a man caught in a crumbling coal mine, and the canaries are dropping like flies."

John held Sherlock's trembling hands together, as if in prayer, to his chest. The tears in Sherlock's sea-glass eyes were tears of frustration, of hatred. He was forced to witness the deliberate desecration of his mind, he saw it in the peeling of the wallpaper, the chipping of the paint on the stairs. Soon, the floor of the halls would buckle, the tile cracking and the wood splintering. His mind palace would creak and shudder, and all he could do was sit in the wreckage and try to hold the walls up.


End file.
